226 Trees, Stars, and Birds 



know? When the moon passes between us and a star, 

 the star would become dim before disappearing if the 

 moon were surrounded with air. Instead of that, the 

 star remains bright until the instant it vanishes. 



The moon must be made of material that is not very 

 dense, for the whole earth weighs about 80 times as 

 much as the moon, although it is only 49 times as large. 

 We know this because the moon's power to attract other 

 bodies is so much less than the earth's attractive force. 

 A boy who weighs 100 pounds on the earth would weigh 

 i6f pounds on the moon; and a baseball could be 

 thrown 6 times as far as on the earth. 



Every part of the moon is successively turned toward 

 the sun as the moon revolves around the earth. As 

 sunshine on the moon is continuous at any one place for 

 about 354 hours, the temperature must become very 

 high. Probably the rocks are heated to such a degree 

 that they would burn you, if you were to touch them. 

 During the equally -long night the surface of the moon 

 becomes very cold. The great change of temperature 

 due to such long days and long nights is made all the 

 greater by the lack of an atmosphere that would act as 

 a shield against great extremes of heat and cold. Up 

 high among the mountains on the earth where the air 

 is rare, the difference in temperature during the day and 

 the night is much greater than at lower levels. 



How the earth would appear from the moon. If 

 people lived on the side of the moon which we see, the 

 earth would be visible to them all the time. It wo.uld 

 never rise or set, but could always be seen in nearly the 

 same direction and at nearly the same altitude, like the 



